Fatal hypertrophic cardiomyopathy associated with an A8296G mutation in the mitochondrial tRNA(Lys) gene

We describe an 8-day-old baby girl presenting a fatal infantile form of hypertrophic obstructive cardiomyopathy, associated with an A8296G mutation in the mitochondrial tRNA(Lys) gene. She was born from a healthy unrelated couple, and was the first infant of dizygotic twins. Soon after birth, she was noted to have tachypnea and generalized hypotonia. She had high levels of lactate and pyruvate, and was diagnosed as having hypertrophic cardiomyopathy using echocardiography. She died by cardiac failure. Mitochondrial DNA analysis was performed by sequencing after PCR-subcloning methods, and the percentage of mutation was measured using PCR-RFLP methods. In various tissues obtained at autopsy, analysis showed a heteroplasmic population of A8296G mutation in the mitochondrial tRNA(Lys) gene in all the tissues examined. Maternal inheritance was demonstrated in the family members. Our data demonstrated that an A8296G mutation in the mitochondrial tRNA(Lys) gene showed clinical heterogeneity from a milder form previously reported as mitochondrial diabetes mellitus, to a more severe form as hypertrophic obstructive cardiomyopathy, according to the spatial distribution of this mutation. Hum Mutat 15:382, 2000.     

线粒体tRNALeu(UUR)A3243G基因突变与2型糖尿病的相关研究

目的　探讨线粒体 t RNALeu( UUR) 32 4 3A→ G突变在中国人 2型糖尿病 (type2 diabetes melli-tus,DM2 )人群中的发生率及其临床特征。方法　随机抽取无血缘关系的 DM2患者 4 2 8例及正常对照 188名 ,采用PCR/ Apa 酶切法进行线粒体基因 t RNAL eu( UUR) 32 4 3A→G突变检测。结果　在 DM2组中发现 2例该基因突变患者 ,在 2例患者的家系中又检出 3例阳性患者。其中例 1及其儿子除患糖尿病外 ,还呈线粒体肌脑病伴乳酸酸中毒及中风样发作综合征表现。基因突变患者的临床特点主要为糖尿病伴或不伴耳聋 ,有家族史 ,呈母系遗传。结论　线粒体基因 t RNAL eu( UUR) 32 4 3A→G突变性糖尿病在中国 DM2人群中的发病率约为 0 .4 7% ,突变患者的临床表型呈一定的异质性。     

Presence of mitochondrial tRNA(Leu(UUR)) A to G 3243 mutation in DNA extracted from serum and plasma of patients with type 2 diabetes mellitus

AIMS/BACKGROUND: An A to G substitution at base pair 3243 in the mitochondrial tRNA(Leu(UUR)) gene (mt3243) is commonly associated with maternally inherited diabetes and deafness, and other diseases. It is possible that cell free mitochondrial DNA exists in serum and plasma from these patients, and these samples might be a source of material for the detection of such mutations. METHODS: Sixteen patients with type 2 diabetes mellitus and 25 healthy subjects were tested for the 3243 mutation by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis. Plasma and serum from the 41 subjects were tested blind, without knowledge of the final diagnosis. RESULTS: PCR amplification of the mtRNA(Leu(UUR)) region in mitochondrial DNA (mtDNA) in serum samples revealed the presence of mtDNA in all samples. After ApaI digestion of the amplified DNA fragments, mt3243 was detected in the serum and plasma samples of the seven patients with diabetes who had previously been found to have this mutation in their leucocyte DNA. None of the serum/plasma samples from the healthy subjects or those patients negative for mt3243 in their leucocytes had this mutation (p < 0.001). In addition, the degree of heteroplasmy of mt3243 appeared to be higher in serum and plasma samples than in leucocytes among mt3243 carriers (p < 0.05). CONCLUSIONS: Therefore, mtDNA and associated mutations are present and detectable in serum and plasma. Plasma and serum might be alternative sources for the molecular diagnosis of mt3243 associated diabetes mellitus, as well as other mitochondrial mediated diseases.     

The mitochondrial A3243G mutation presenting as severe cardiomyopathy.

A 6 year old Portuguese boy with dilated cardiomyopathy had abundant ragged red fibres in muscle (20% of total) and severe lactic acidosis. Molecular genetic analysis showed the A to G transition in the mitochondrial transfer RNALeu(UUR) gene at nt 3243 ("MELAS mutation"), which accounted for 88% and 68% of the total mtDNA in his muscle and blood, respectively. Molecular studies in blood from 16 maternal relatives identified lower percentages of the mutation only in the oligo-symptomatic mother and brother. This case reinforces the notion that cardiomyopathy can be the presenting and predominant clinical expression of the A3243G mutation.     

Barth's syndrome-like disorder: a new phenotype with a maternally inherited A3243G substitution of mitochondrial DNA (MELAS mutation)

An Argentine male child died at 4.5 years of age of a lethal mitochondrial disease associated with a MELAS mutation and a Barth syndrome-like presentation. The child had severe failure to thrive from the early months and for approximately two years thereafter. In addition, the patient had severely delayed gross motor milestones, marked muscle weakness, and dilated cardiomyopathy that progressed to congestive heart failure. He also had persistently elevated urinary levels of 3-methylglutaconic and 2-ethylhydracrylic acids and low blood levels of cholesterol. Detailed histopathologic evaluation of the skeletal muscle biopsy showed high activity of succinate dehydrogenase, a generalized decrease of COX activity, and abundant ragged-red fibers. Electron microscopic studies revealed multiple mitochondrial abnormalities in lymphocytes and monocytes, in the striated muscle, and in the postmortem samples (muscle, heart, liver, and brain). Biochemical analysis showed a pronounced and constant lactic acidosis, and abnormal urinary organic acid excretion (unchanged in the fasting and postprandial states). In addition, in CSF there was a marked increase of lactate and beta-hydroxybutyrate (beta-HOB) and also a high systemic ratio beta-HOB/acetoacetate. Enzymatic assay of the respiratory chain in biopsied muscle showed 10% of complex I activity and 24% of complex IV activity compared with controls. Molecular studies of the mitochondrial genome revealed an A to G mutation at nucleotide pair 3243 in mitochondrial DNA, a well-known pathogenetic mutation (MELAS mutation) in all the patient's tissues and also in the blood specimens of the probands mother and sibs (4 of 5). The diagnosis of MELAS mutation was reinforced by the absence of an identifiable mutation in the X-linked G4.5 gene of the propositus. The present observation gives additional evidence of the variable clinical expression of mtDNA mutations in humans and demonstrates that all clinical variants deserve adequate investigation to establish a primary defect. It also suggests adding Barth-like syndrome to the list of phenotypes with the MELAS mutation.     

A new mtDNA mutation in the tRNALeu(UUR) gene associated with maternally inherited cardiomyopathy

We report a new mutation, a C to T transition at nt 3303 of mtDNA, in seven members of a family with cardiomyopathy and myopathy: the proband and two siblings had fatal infantile cardiomyopathy, whereas in three maternal relatives the disease manifested later in life as sudden cardiac death or as mitochondrial myopathy with cardiomyopathy. The mutation was homoplasmic in all tissues (including blood) from the proband and her brother, but heteroplasmic in blood from five oligosymptomatic or asymptomatic maternal relatives. This mutation disrupts a conserved base pair in the aminoacyl stem of the tRNA^Leu(UUR). None of 70 controls carried the mutation. Our data indicate that this mutation is the genetic cause of the disorder in this family, and confirm that the tRNA^Leu(UUR) is a “hot spot” for mutations in mtDNA. © 1994 Wiley-Liss, Inc.     

Barth's syndrome‐like disorder: A new phenotype with a maternally inherited A3243G substitution of mitochondrial DNA (MELAS mutation)

An Argentine male child died at 4.5 years of age of a lethal mitochondrial disease associated with a MELAS mutation and a Barth syndrome‐like presentation. The child had severe failure to thrive from the early months and for approximately two years thereafter. In addition, the patient had severely delayed gross motor milestones, marked muscle weakness, and dilated cardiomyopathy that progressed to congestive heart failure. He also had persistently elevated urinary levels of 3‐methylglutaconic and 2‐ethylhydracrylic acids and low blood levels of cholesterol. Detailed histopathologic evaluation of the skeletal muscle biopsy showed high activity of succinate dehydrogenase, a generalized decrease of COX activity, and abundant ragged‐red fibers. Electron microscopic studies revealed multiple mitochondrial abnormalities in lymphocytes and monocytes, in the striated muscle, and in the postmortem samples (muscle, heart, liver, and brain). Biochemical analysis showed a pronounced and constant lactic acidosis, and abnormal urinary organic acid excretion (unchanged in the fasting and postprandial states). In addition, in CSF there was a marked increase of lactate and β‐hydroxybutyrate (β‐HOB) and also a high systemic ratio β‐HOB/acetoacetate. Enzymatic assay of the respiratory chain in biopsied muscle showed 10% of complex I activity and 24% of complex IV activity compared with controls. Molecular studies of the mitochondrial genome revealed an A to G mutation at nucleotide pair 3243 in mitochondrial DNA, a well‐known pathogenetic mutation (MELAS mutation) in all the patient's tissues and also in the blood specimens of the probands mother and sibs (4 of 5). The diagnosis of MELAS mutation was reinforced by the absence of an identifiable mutation in the X‐linked G4.5 gene of the propositus. The present observation gives additional evidence of the variable clinical expression of mtDNA mutations in humans and demonstrates that all clinical variants deserve adequate investigation to establish a primary defect. It also suggests adding Barth‐like syndrome to the list of phenotypes with the MELAS mutation. © 2001 Wiley‐Liss, Inc.     

一个母系遗传非综合征型耳聋家系线粒体12S rRNA G709A位点的突变分析

目的 通过对一个母系遗传非综合征型耳聋家系进行线粒体DNA(mitochondrial DNA,mtDNA)12S rRNA、tRNA~(Ser(UCN))以及核基因GJB2突变分析,研究mtDNA突变与遗传性耳聋的相关性.方法 临床听力测试以明确诊断,收集非综合征型遗传性耳聋家系中18例母系成员和53名对照(包括6名父系亲属、7名配偶对照和40名当地无关对照)外周静脉血样本,采用聚合酶链反应和测序技术对mtDNA 12S rRNA、tRNA~(ser(UCN))和GJB2基因进行突变分析,并对发现的基因突变进行计算机辅助的二级结构模拟分析.结果 测序结果表明,此家系线粒体DNA 12S rRNA存在mtDNA G709A点突变,该突变未见报道;无tRNA~(Ser(UCN))基因突变;对GJB2突变分析发现4例具有299-300 delAT.计算机分析显示12SrRNA的二级结构中第8、9茎环结构发生改变.结论 家系中8例耳聋患者都具有线粒体12S rRNAG709A位点的突变,该突变在正常人群中具有高度保守性,提示GT09A点突变与母系遗传家系成员的进行性耳聋具有相关性;10例具有G709A突变的母系遗传家系成员未出现耳聋的临床表现,提示G709A点突变可能在其他核修饰基因的协同作用下参与了听力损害的过程.     

Level of heteroplasmy for the mitochondrial mutation A3243G correlates with age at onset of diabetes and deafness

The mitochondrial mutation A3243G has been shown to be associated with a syndrome of diabetes mellitus and sensorineural hearing loss. Using a solid-phase-based sequencing method we have investigated the relation between the proportion of mutant mitochondrial genomes and the time of disease onset among members of three families where the mutation segregates. A striking association was observed between the level of heteroplasmy and time of onset of disease, particularly hearing loss. Accordingly, this syndrome shares features of diseases caused by dynamic mutations in that variable transmission of the level of heteroplasmy between generations influences disease severity. Hum Mutat 12:52–58, 1998. © 1998 Wiley-Liss, Inc.     

The level of the mitochondrial mutation A3243G decreases upon ageing in epithelial cells from individuals with diabetes and deafness

We have in a longitudinal study determined the proportion of the mitochondrial A3243G mutation in DNA obtained from cervical cell samples collected from three individuals affected with mitochondrial diabetes and hearing loss during a period of up to 18 years. Using the minisequencing method we were able to sensitively determine the proportion between mutant and normal mitochondrial DNA. Our results demonstrate a constant decrease in the levels of the pathogenic mutation in mitotic tissues of affected individuals with time.     

Pancreatic exocrine dysfunction associated with mitochondrial tRNA(Leu)(UUR) mutation.

We report on pancreatic exocrine dysfunction in families that have the mitochondrial tRNA(Leu)(UUR) gene mutation. These families exhibited maternally inherited diabetes mellitus (DM) and an A to G substitution at nt 3243 of the mitochondrial tRNA(Leu)(UUR) gene (A3243G mutation). Pancreatic necropsy samples from one proband showed accumulation of degenerated mitochondria in pancreatic acinar cells. Pancreatic exocrine dysfunction was recognised by a functional pancreatic study. This study indicates that exocrine pancreatic dysfunction may be associated with the A3243G mutation.     

Prevalence of A-to-G mutation at nucleotide 3243 of the mitochondrial tRNALeu(UUR) gene in Japanese patients with diabetes mellitus and end stage renal disease

The A-to-G mutation at nucleotide 3243 of the mitochondrial tRNA ^Leu(UUR) gene (mt.3243A>G) is associated with both diabetes mellitus and myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Recently, this mutation was found in three diabetic subjects with progressive kidney disease, suggesting that it may be a contributing factor in the development of kidney disease in patients with diabetes. The aim of this study was to evaluate the contribution of this mutation to the development of end stage renal disease (ESRD) in patients with diabetes. The study group consisted of 135 patients with diabetes and ESRD. The control group consisted of 92 non-diabetic subjects with ESRD who were receiving hemodialysis. The mt.3243A>G mutation was detected by polymerase chain reaction-restriction frag-ment length polymorphism (PCR-RFLP). We found the mt.3243A>G mutation in eight patients (8/135; 5.9%), all of whom were initially diagnosed with type II diabetes. Five of the eight patients were subsequently also diagnosed with MELAS. We did not find the mutation in any of the 92 non-diabetic subjects with ESRD. The prevalence of this mutation was 6.5-fold higher in patients with diabetes and ESRD than in those with diabetes alone (8/135 vs 5/550, respectively; χ² = 13.704; P = 0.0002). The mt.3243A>G mutation may be a contributing genetic factor in the development of ESRD in Japanese patients with diabetes. Received: November 29, 2000 / Accepted: February 27, 2001     

糖尿病家系的线粒体基因tRNALeu(UUR)A3243G突变分析

目的 分析线粒体基因tRNALeu(UUR)A3243G突变的糖尿病家系中发病规律.方法 筛选临床疑似线粒体糖尿病家系,采用PCR、DNA直接测序技术对3个家系19例临床疑似线粒体基因突变糖尿病家系进行线粒体基因突变高发区域tRNALeu(UUR)基因的检测.结果 3个家系发现与糖尿病发病有关的突变位点均位于nt3243A→G突变,且家系中大部分患者伴有消瘦、耳聋、β细胞功能低下、发病年龄低的特点.结论 线粒体tRNALeu(UUR)基因3243位点A→G突变可导致糖尿病和耳聋.     

线粒体tRNALeu(UUR)基因nt3243A→G突变糖尿病临床特点分析

目的 了解线粒体tRNALeu(UUR)基因nt3243A→G突变在上海及江浙地区家族性糖尿病人群中的发生率及其临床特点.方法 应用聚合酶链反应-限制性片段长度多态结合直接测序方法对随机抽取的无亲缘关系的770个糖尿病家系的先证者进行线粒体tRNA<'Leu(UUR)>基因nt3243A→G突变的筛查,并进一步对阳性先证者家系进行家系遗传学及临床特点分析.结果 在770个糖尿病先证者中发现13例(1.69%)nt3243A→G突变.13个先证者家系的一级亲属中共检出32例3243突变携带者,其中24例为糖尿病,8例糖耐量正常,17例伴不同程度听力减退.24例糖尿病患者多呈消瘦体型,有18例呈典型母系遗传,13例伴胰岛素抵抗,15例伴听力障碍,14例应用胰岛素治疗.结论 上海及江浙地区家族性糖尿病人群线粒体3243点突变检出率是1.69%,线粒体糖尿病患者的临床特点是:(1)多数呈母系遗传,少数可为散发;(2)多于45岁以前发病;(3)体型多偏瘦;(4)胰岛β细胞分泌功能明显降低,部分患者同时伴有胰岛素抵抗;(5)多数患者伴神经性听力障碍或神经性耳聋.     

Prevalence of the mitochondrial DNA A1555G mutation in sensorineural deafness patients in island Southeast Asia

A mtDNA A1555G base substitution in a highly conserved region of the 12S rRNA gene has been reported to be the main cause of aminoglycoside induced deafness. This mutation is found in approximately 3% of Japanese and 0.5–2.4% of European sensorineural deafness patients. We report a high prevalence (5.3%) of the A1555G mutation in sensorineural deafness patients in Sulawesi (Indonesia). Our result confirms the importance of determining the prevalence of the mtDNA A1555G mutation in different populations, and the need for mutation detection before the administration of aminoglycoside antibiotics.     

A novel mutation in the mitochondrial tRNA(Ser(UCN)) gene in a family with non-syndromic sensorineural hearing impairment

We describe a family with non-syndromic sensorineural hearing impairment inherited in a manner consistent with maternal transmission. Affected members were found to have a novel heteroplasmic mtDNA mutation, T7510C, in the tRNA^Ser(UCN) gene. This mutation was not found in 661 controls, is well conserved between species, and disrupts base pairing in the acceptor stem of the tRNA, making it the probable cause of hearing impairment in this family. Sequencing of the other mitochondrial tRNA genes did not show any other pathogenic mutations. Four other mutations causing hearing impairment have been reported in the tRNA^Ser(UCN) gene, two having been shown to affect tRNA^Ser(UCN) levels. With increasing numbers of reports of mtDNA mutations causing hearing impairment, screening for such mutations should be considered in all cases unless mitochondrial inheritance can be excluded for certain.


Keywords: hearing impairment; mtDNA mutation; tRNA^Ser(UCN)